The need exists of maintaining the inner temperature of a house, not yet fully satisfied, within a suitable and comfortable range. High temperature cycles during summer time in a number of regions make it necessary to install and operate air conditioning equipment with the consequent cost of energy therefor. In order to save energy, the walls and roofs of buildings are normally insulated with coatings of low thermal conductivity, for example polyurethane and polystyrene. These materials however imply a high application cost because they require an additional coating of other materials to prevent degradation caused by solar radiation, and also these polymers have the disadvantage of being flammable.
There are already on the market a variety of coatings which may be applied to the walls and roofs of buildings exposed to solar radiation for lowering the temperature in said buildings. In general, these coatings merely comprise a light colored pigment, since it is well known that dark-colored materials absorb more radiation heat than light-colored materials. As more radiation is reflected by the coating, less heat accumulates in the roofs and walls; and therefore the inner temperature is lower because less heat is radiated to the interior space of said buildings.
Additionally, such coatings may comprise materials of very low thermal conductivity in order to provide a heat insulating effect, for example, glass microspheres of a particle size between 50 and 150 microns, as described in U.S. Pat. No. 4,623,390.
The coating of the present invention provides, in addition to the effects of thermal insulation and of high radiation percentage reflectance, a heat dissipating effect derived from a a hygroscopic ingredient, which absorbs water from ambient air, which water later on evaporates when solar radiation increases the temperature of said coating. Thus some of the solar energy that would have gone to raise the temperature of the coated building is instead diverted into providing the latent heat of evaporation used in drying out the hygroscopic coating. In other words, the coating of the invention permits the evaporation of the absorbed humidity and therefore heat is dissipated to the environment further decreasing the temperature of the building roof and consequently also the inner temperature in said building.
British patent No. 762,272 discloses a composition of a coating utilized for solving a typical problem of water condensation in cold climate regions (where the exterior temperature is lower than the temperature of the interior of buildings, and the inner temperature is made comfortable by some heating equipment). In these regions, it is desired as much as possible to prevent heat flow from the inner space to the exterior environment. For this purpose, the roofs and walls of buildings are coated with thermal insulating materials. However, when the temperature of the inner surfaces of roofs and walls reaches the dew point of the air inside the building, water is condensed and drops from the ceiling etc. This patent proposes a solution to this problem by coating the inner surfaces with a coating comprising a hygroscopic material, diatomaceous earth (diatomite) or other inorganic hydrophilic materials, for example, pumice, basic magnesium carbonate and fuller earth. These materials are porous and absorb the condensed water thus avoiding drops from falling. The composition disclosed in this prior art patent is essentially: a film-forming agglomerating material, cellulose compounds emulsified in water, water forming the continuous phase and an inorganic material of low thermal conductivity (k<0.8) dispersed in the mixture comprising the hydrophilic cellular material in an amount of 10% to 45% by weight, which can be diatomite. The thickness of the coating in the tests described in this patent was 0.6 mm.
U.S. Pat. No. 4,442,242 discloses the composition of a coating for surface insulation with the purpose of preventing or decreasing formation of condensed water. This coating is applied to the treated surface as a film having a thickness between 0.5 and 10 mm, preferably from 1 to 5 mm. This patent describes a film-forming binding material dispersed in an aqueous vehicle having granules of heat-expanded perlite which can form an insulating and water absorbing coating. The coating contains from 5% to 20% perlite granules by weight with a particle size between 0.01 mm to 1.5 mm before its application. The coating of this patent is capable of absorbing water but is not utilized for decreasing the inner temperature of a building and is used as applied in thick layers, therefore representing a higher cost. This coating is also utilized in buildings where heat flows from the inner part of the building to the exterior environment.
Applicants have not found a prior art reference suggesting or disclosing the concept of the present invention, which comprises to coat the roofs and walls of a building, house or similar construction with a thin layer of a coating which dissipates the accumulated heat by the evaporative effect of water absorbed by a hygroscopic material contained in said coating; and where the water is absorbed from the ambient air and where the absorption-evaporation cycle is repeated by the changing dynamics of relative humidity of ambient air and the temperature increase of said coating by being exposed to solar radiation.
It is therefore an object of the present invention to provide a method and a coating for decreasing the inner temperature of a building, house or similar construction, exposed to solar radiation, by means of a heat dissipation effect.
It is another object of the present invention to provide a method and a coating for decreasing the energy consumption of air conditioning equipment by decreasing the amount of heat radiated to the interior of a building by the roofs and walls thereof.
It is a further object of the present invention to provide a method and a coating of low cost for rendering more comfortable buildings and houses in hot-climate regions, even if they do not have air conditioning equipment.
Other objects of this invention will be pointed out below in this specification or will be evident to those skilled in the art.